Various clinical studies have indicated that preemptive analgesia can effectively attenuate pain and reduce analgesic requirements postoperatively,1,2 with clinical effects varying by anatomic area and specific surgical procedure performed.3 In the gynecologic literature, a randomized, double-blinded, placebo-controlled trial of preemptive analgesia in laparoscopy concluded that administration of bupivacaine before laparoscopy resulted in decreased postoperative pain and medication requirements.4 Preemptive ischiorectal fossa blockade has been shown to reduce postoperative pain intensity and analgesic consumption after hemorrhoidectomy.5 Pudendal nerve blockade has been used successfully for both penile prosthetic surgery and circumcision.6,7 It has also been used in obstetric practice as a low-risk, low-cost anesthetic technique effectively reducing perineal and vaginal discomfort during repair of obstetric lacerations.8
Although pudendal nerve blockade has been employed safely during pelvic reconstructive surgery,9 it has not yet been tested as a preemptive analgesia for reducing pain intensity after this procedure. Postoperative pain after vaginal reconstruction is commonly localized to the posterior vulva and perineum; dull discomfort may also originate from the region of the sacrospinous ligament and pelvic floor. Pudendal nerve blockade is administered at the sacrospinous ligament and provides highly effective and safe anesthesia to the vulva, lower vagina, and perineum. We, therefore, hypothesized that preemptive pudendal nerve block may significantly decrease pain and consumption of narcotic analgesia after pelvic reconstructive surgery.
MATERIALS AND METHODS
All women who were scheduled to undergo transvaginal pelvic reconstructive surgery under general anesthesia between November 2001 and December 2004 at the Evanston Continence Center were invited to enroll in the study. Inclusion criteria were American Society of Anesthesiologist (ASA) physical status I-II, age between 20 and 80 years, and the ability to speak and read English. Exclusion criteria included an intolerance to local anesthetic agents or narcotics, coagulation disorders, ASA physical status of more than II, history of a major psychiatric disorder, chronic pain syndromes, history of substance abuse, and current opioid use. Planned procedures for concurrent urinary incontinence did not preclude participation in the trial. All subjects underwent a comprehensive physical and pelvic examination, including cotton-tipped swab testing and pelvic organ prolapse assessment by the pelvic organ prolapse quantification (POP-Q)10 system.
Subjects were randomly allocated to receive preemptive pudendal nerve blockade with 10 mL of either 0.25% bupivacaine (Marcaine, Abbott Hospital Products, Abbott Park, IL) or normal saline to each side. The allocation schedule was determined by a computer-generated random-numbers table using concealed opaque envelopes. The patients, surgeons, anesthesiologists, and recovery personnel were blinded to the injected material, which was drawn by a separate research nurse. All subjects signed an informed consent approved by the Institutional Review Board Committee for Human Subjects before randomization. All subjects received antibiotic prophylaxis with cefoxitin 2 g intravenously within an hour before surgery. All surgeries were performed transvaginally under general anesthesia induced by intravenous fentanyl 2 μg/kg and propofol 2 mg/kg. Atracurium 0.5 mg/kg was administered to facilitate tracheal intubation. Anesthesia was then maintained with nitrous oxide 70% and isoflurane 0.5–1.0% in oxygen. The lungs were mechanically ventilated, and the end-tidal carbon dioxide concentration was maintained between 5.0% and 5.5%. Two attending physicians (P.K.S. and R.P.G.) supervised all surgeries. Patients were placed in Allen's stirrups in the dorso-lithotomy position. After general anesthetic induction, prepping, and draping, each patient received a 10-mL pudendal nerve block injection on each side as previously described.11 A tubular director that allows 1.0–1.5 cm of a 15-cm-long, 22-gauge needle to protrude beyond its tip was used to guide the needle into position over the pudendal nerve. The end of the director was placed against the vaginal epithelium just beneath the tip of the ischial spine. The needle was pushed beyond the tip of the director, and 5 mL of the anesthetic solution was injected. The needle was then advanced 1 cm posterior and lateral, and another 5 mL of the anesthetic solution was injected into this region. Aspiration was attempted before every injection to guard against intravascular infusion. After 2 hours, if surgery was still in progress, an additional 5-mL pudendal nerve block was administered on each side.
After surgery, all patients were monitored in the postanesthesia care unit for 1–2 hours, after which time the patient returned to the postoperative ward. Patients were assessed immediately upon arrival in the postanesthesia care unit and were connected to a patient-controlled analgesia pump system (Abbott Life Care Infuser, Abbott Laboratories, Chicago, IL). Every 5–10 minutes, patients were asked by a nurse blinded to the group allocation whether they were in need of pain relief. An affirmative response was followed by a 1-mg intravenous bolus of hydromorphone (Dilaudid, Abbott Laboratories, Chicago, IL). This procedure was repeated until the patients were alert enough to begin self-administration with the patient-controlled analgesia pump button. The patient-controlled analgesia was set to deliver a 0.3-mg intravenous bolus of hydromorphone with a lockout time of 10 minutes and no continuous background infusion. This regimen was continued for 18 hours postoperatively, during which time no other analgesics were administered, unless the patient asked for them specifically. Hydromorphone consumption in milligrams was calculated on an hourly basis from hard copy or computerized records of the 24-hour study period. After 18 hours, standard oral analgesic regimen of ibuprofen (600 mg tablets every 6 hours, as needed) and hydrocodone (500 mg tablets, every 4 hours as needed) was initiated.
Postoperative pain intensity was assessed by using a validated visual analog pain scale12 at 1, 3, 5, 7, 18, and 24 hours after surgery. This pain scale provides a validated and minimally intrusive measure of pain intensity, consisting of a 10-cm vertical line with the 2 end points labeled “no pain” and “worst possible pain.” The patient is required to mark the 10-cm line at a point that corresponds to the present level of pain intensity. The distance in centimeters from the low end of the visual analog scale and the patient's mark are used as a numerical index of pain intensity. To ensure that the questions were asked in the same way each time, the nursing staff was instructed to phrase the questions in a standardized fashion, using specific wording, as follows: “How bad is your pain? Please mark your pain intensity on the pain scale from 0 to 10, where 0 indicates no pain and 10 indicates the worst possible pain.” Patients were also interviewed by the nursing staff regarding any adverse effects of the analgesic medications or pudendal block, using the wording: “Do you have any other complaints apart from the pain?”
Analgesic requirements were consistently recorded at 3, 7, 18, and 24 hours after surgery. The primary outcome measures of the study were visual analog pain scores and postoperative analgesic consumption. Secondary measures included adverse effects of the pudendal block, medical and surgical complications, and length of hospital stay.
Power calculations were performed before patient recruitment, based on a previous report on the effect of preemptive epidural analgesia on morphine consumption after lower abdominal and pelvic surgery.13 In that study, the mean cumulative morphine consumptions were 55 mg and 71 mg in the preemptive analgesia and control groups, respectively, with a standard difference of 28 mg. The reduction in morphine consumption, therefore, amounted to a 30% saving in favor of the preemptive analgesia group. Standard power calculations (STPLAN 4.0; The University of Texas, Houston, TX) based on these data indicated that 50 women would be required for each study group to detect a 20% difference with 80% power and 5% significance. Demographic, clinical, surgical, and anesthetic outcomes of each group were compared using t tests, χ2, and Fisher exact tests, where appropriate. Visual analog pain scores were compared using repeated measures analysis of variance. P values < .05 were considered statistically significant for all comparisons. The Windows version of SPSS 11.0.1 (SPSS Inc, Chicago, IL) was used for data management and statistical analysis.
One hundred ten women enrolled in the study, of whom 4 dropped out before randomization (two cancelled their surgery, one decided to undergo spinal anesthesia, and one gave no specific reason). Of the 106 patients who had been randomized for the study, 2 patients from each group dropped out after randomization (two underwent spinal anesthesia and two gave no specific reason). One hundred two patients received preemptive pudendal block analgesia, 51 with bupivacaine 0.25% and 51 with saline 0.9% (Fig. 1).
The 2 groups did not differ in baseline demographic and clinical characteristics nor in previous surgical interventions (Table 1). No significant differences were noted between the 2 groups in surgical procedures, total volume of pudendal block injected, fentanyl and propofol dose, total blood loss, operative time, or surgical and medical complications (Table 2). Thirty-two patients (63%) from the bupivacaine group and 30 patients (59%) from the saline group received a second pudendal block injection due to prolongation of their surgery beyond 2 hours. There were no significant differences between the 2 groups in mean postoperative pain scores and consumption of intravenous hydromorphone (0–3 hours, 1.84 versus 1.77 mg; 4–7 hours, 1.19 versus 1.20 mg; 8–18 hours, 2.89 versus 2.35 mg) (Table 3). Additional boluses of hydromorphone (18% versus 18%) and ketoralac (12% versus 8%), as well as mean oral hydrocodone (10.6 mg versus 12.7 mg) and ibuprofen (630 mg versus 762 mg) consumption in the first 24 hours after surgery were not significantly different between the 2 groups. There were no significant differences in mean total hospital stay between the 2 patient groups (39.6 hours versus 37.3 hours) (Table 3). There were no complications directly associated with the pudendal nerve blockade in any of the study patients. No specific surgical procedures were found to be associated with higher postoperative pain intensity or increased consumption of narcotic analgesia.
These results indicate that preemptive pudendal nerve blockade does not reduce pain intensity or the consumption of narcotic analgesia following transvaginal pelvic reconstructive surgery. Pelvic reconstructive surgery accounts for an increasing operative volume each year because of the widespread prevalence of pelvic prolapse and incontinence within the aging female population. Up to 11% of women will undergo major prolapse or incontinence surgery by age 79.14 Therefore, identifying safe techniques that enhance patient recovery in a cost-effective manner may have the potential for widespread application.
The concept of preemptive analgesia to reduce the magnitude and duration of postoperative pain was introduced in 1983 by Woolf,15 who showed evidence for a central component of postinjury pain hypersensitivity in experimental studies. Noxious events associated with surgery induce a state of central neural sensitization in the spinal cord. After surgery, the flow of afferent input impinges on these sensitized neurons, which then amplify the peripheral signal and transmit it onward to the brain. The pain that accompanies these events is therefore more severe than it otherwise would have been if the spinal cord cells had been blocked at the time of surgery. The principle of preemptive analgesia is therefore to apply antinociceptive treatment before surgical trauma to prevent spinal hypersensitization.
A large body of animal data demonstrate that various antinociceptive techniques applied before injury were more effective in reducing the postinjury central sensitization phenomena than administration after injury.16 However, when tested clinically in humans, the efficacy of these techniques has been less than optimal, depending on the anatomic area and type of surgery. A randomized, double-blind study from Japan3 evaluated the preemptive use of epidural morphine in 6 surgery types and found the technique effective for mastectomy and limb surgery, but not for surgeries involving laparotomy. Presurgical axillary block has been associated with lower required doses of inhalation agents in pediatric orthopedic surgery.17 Preemptive ischiorectal fossa block, using local anesthesia, was evaluated in another randomized, prospective, double-blind trial in 20 patients undergoing hemorrhoidectomy, a procedure commonly associated with severe pain in the immediate postoperative period. The technique was associated with significantly decreased pain scores and postoperative analgesic requirements.5 Another randomized, double-blind, placebo-controlled trial found that preemptive intraperitoneal bupivacaine reduced postoperative pain during cholecystectomy. In contrast, other studies have found no advantage for preemptive analgesia in patients undergoing nephrectomy18 or thoracotomy.19 Moiniche et al20 performed a meta-analysis of the efficacy of preemptive analgesia in different anatomical sites using different surgical and anesthetic techniques and concluded that the majority of the data does not support the use of this technique for postoperative pain relief.
In the gynecologic and obstetric literature, only a few studies have investigated the efficacy of preemptive analgesia, with conflicting results. One study21 found that a single dose of morphine given before abdominal hysterectomy was more effective in relieving postoperative pain than when given thereafter. Another study22 found that preemptive administration of epidural lidocaine and fentanyl was associated with a significantly lower rate of morphine use and reduced hyperalgesia following transabdominal gynecologic surgery. Kwok et al23 found that a small dose of preemptive ketamine decreased pain after gynecologic laparoscopic surgery. Wittels et al24 found that injection of a local anesthetic into the fallopian tubes before laparoscopic tubal ligation was effective in decreasing postoperative pain. Niv et al25 reported a decrease in postepisiotomy pain with preemptive epidural morphine. In contrast, Lam et al26 found that preemptive injection of lidocaine into the incisions before diagnostic laparoscopy was less effective in reducing postoperative pain than when injected postoperatively. Similarly, Grube et al27 found no benefit in preemptive analgesia for gynecologic laparoscopy. Another trial investigated preemptive ilioinguinal iliohypogastric nerve block in patients undergoing cesarean delivery28 and demonstrated no significant postoperative pain relief.
In this study we chose to evaluate the postoperative analgesic effect of preemptive pudendal block in women undergoing transvaginal pelvic reconstructive surgery. The reasons for choosing pudendal block were its simplicity, low risk, low cost, and wide-spread use in obstetric and gynecologic practice.8 Pudendal block has also been employed safely during pelvic reconstructive surgery by the vaginal route. Miklos et al9 reported on its successful use as a local anesthetic adjunct among 20 patients undergoing vaginal prolapse repair who were not medically approved for general anesthesia. Potential complications associated with pudendal block include pelvic hematomas and rare infections.29 Adverse reactions of the local anesthetic used are rare and may include cardiovascular and neurological symptoms. In this study each patient received a maximal bupivacaine dose of 75 mg, which is within the therapeutic range of this drug. To reduce the risk of adverse reactions resulting from intravascular injection, negative suction was routinely applied to each syringe before injection. With these precautions taken, we encountered no complications directly related to the pudendal nerve block procedure or to the local anesthetic in any of the study patients.
With regard to the use of pudendal block for preemptive analgesia in gynecologic and obstetric surgery, we performed a MEDLINE search of the English literature from 1966 to February 2005, using the terms “pudendal,” “preemptive,” and “prophylactic,” and found no relevant reports. The current study is the first to explore the use of preemptive pudendal block for transvaginal pelvic reconstructive surgery. The study could not demonstrate any beneficial effect for this technique over placebo in either postoperative pain control or narcotic consumption. A possible explanation for these negative findings may be insufficient afferent inhibition of the surgery's nociceptive stimuli by the pudendal block. We could not assess the effectiveness of the block immediately after injection because it was performed while the patients were under general anesthesia. Another possible explanation is that the duration of the block may have been too short to achieve effective preemptive analgesia. Since central sensitization is induced not only during surgery, but also postoperatively by inflammatory processes, a prolonged block of ongoing nociceptive input seems desirable. In fact, in a study in rats, a long-lasting tonicaine nerve block administered 5 hours after noxious stimulation both reversed early and prevented the development of late (more than 24 hours) hyperalgesia.30 It could, therefore, be speculated that the pudendal block used in the present study did not act long enough to prevent central sensitization and, thus, pain in the postoperative inflammatory phase.
Another possible explanation is that transvaginal pelvic reconstructive surgery might generate a noxious input that is too weak to produce detectable differences between the study groups. Conversely, a postoperative narcotic administration that is too vigorous could also mask the pudendal block's effect, but the fact that all subjects received a patient-controlled analgesia pump with no loading or background infusion makes this explanation less likely. In fact, the patient-controlled analgesia in our study seemed to be an appropriate method of allowing patients to independently titrate their narcotic consumption with minimal adverse reactions. The study was designed and powered to detect a 20% difference in postoperative narcotic consumption, and therefore smaller differences could still be overlooked using this design. Finally, some psychosocial variables that may affect pain perception, such as the extent of social support, mental health status, degree of optimism, coping style, and mood, were not assessed in this study and could have affected its results.
Despite these limitations, this study has substantial strengths inherent to its design. It is the only randomized, double-blind, placebo-controlled trial to examine the effects of preemptive pudendal nerve block on pain after transvaginal pelvic reconstructive surgery. It is, therefore, the only trial to provide level I evidence on this topic. The study used a validated scale (the visual analog pain scale) to assess pain intensity, which adds to the soundness of its results.
In conclusion, preemptive pudendal nerve blockade does not relieve pain after transvaginal pelvic reconstructive surgery. Different techniques and doses of preemptive and nonpreemptive analgesia should be further investigated with the hope of finding more efficient and cost-effective ways of relieving pain and enhancing recovery in this rapidly growing patient population.
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